All vendors and manufacturers of comestibles and pharmaceuticals routinely conduct sample testing of their products to determine their purity and safeness for human consumption. A part of such studies entails the microbiological examination of a number of samples taken from a given production run or lot. The number of samples and the quantity of each sample withdrawn from a production lot vary, depending upon the type of fluid that is being examined, as well as the particular procedures used by a manufacturer.
The various food industries utilize different methods and techniques in performing sample testing. A great deal of scientific analysis goes into each particular test. The testing is expensive and time-consuming; very often, it does not even provide an accurate assessment of the risk of microbial contamination. Of the many sampling techniques, none is well understood or universally respected, despite all of the scientific data and all of the advances in mathematical and statistical analysis. It is not uncommon to find that many companies use more than one method of analysis, because any one given method simply cannot be relied upon to provide an accurate picture of contamination for all products. The necessity for multiple testing bears consequences relating to the marketability of the product, since these costs, too, must be factored into the final product price.
Part of the aforementioned problem lies in the constraints that each particular foodstuff or pharmaceutical places upon the sampling methodology. Fluids that usually provide good test results are those that can be filtered through a membrane with sufficiently fine pores (so as to retain microorganisms) and which allow for large-quantity sampling (100 ml or more). The membrane is then placed on a nutrient medium, which is then incubated to provide microbial colony counts.
Fluids that contain pulp (such as fruit juice) or emulsions (such as dairy products) or those that are viscous (such as syrups and concentrates) usually block membrane filters. Direct plating techniques are used for these types of fluids. The direct plating technique, however, is typically limited by the amount of liquid that the agar of the nutrient medium can absorb. This is usually about 5 ml. Small-volume sampling is particularly troublesome when the bacterial count is low. The smaller the amount of liquid that is tested, the greater the risk of making an improper assessment of microbial contamination.
It is typical for extremely small samples (one ml) of dairy products to be plated on the agar, which makes testing problematical. In addition, when plated, the pulp particles of fruit juices may in some cases be mistaken for microbial colonies, thus giving rise to false data and improper assessment of the microbial contamination.
For organisms that tend to form chains or clumps, techniques such as those based on ATP bioluminescence tend to produce different results than do the plating methods. Plating methods count such organisms as single colonies, while ATP bioluminescence renders results based on the total number of cells in a sample.
Obviously, the many different analyses make comparisons difficult. The non-uniformities in data and procedure make risk assessments confusing and enigmatic. This is particularly true when microbial contamination is low. As mentioned, small-quantity sampling of liquids having low microbial concentrations creates an extremely high risk of inaccurately assessing what could be a potential problem.
It is now routine practice to assume that microbes in fluids are randomly dispersed throughout. the total volume. A number of studies have recently found that the distribution pattern is either not significantly different from or very close to a Poisson distribution. It would, therefore, make sense to fashion a method that would utilize this distribution.
The present invention incorporates a computer program and follow-up technique for improving the microbial analysis of fluids.
The invention allows for the simulation of microbial sampling, based on a Poisson distribution, thereby improving the ability to make comparisons of various sampling strategies.
The current invention also allows the practitioner to explore the effects of organism growth, death or stasis. Current testing techniques rarely investigate these possibilities, due to the added costs and inconvenience of varying the conditions required to obtain this type of data.
The invention greatly reduces the complexity of the testing problem, leading to new insight into what procedures provide good sampling practices. For example, it has always been a standard statistical technique to increase the number of tests in order to provide greater accuracy. The present invention reflects the discovery, however, that, for low concentrations of bacterial contamination, it is preferable to analyze larger volumes of liquid, rather than a greater number of samples. In the industries utilizing this invention, an insight such as this will greatly improve future microbial assessments.